For the intake of medication for obstructive airways diseases, inhalers are well known. There are different types of inhalers, and each type has its own advantages and disadvantages. Nebulizer/compressor systems require minimal patient cooperation and coordination but are cumbersome and time-consuming to use. Metered Dose Inhalers (MDIs) are quick to use and highly portable, but require patient training to ensure coordination for proper use. Another type of inhalers are dry powder inhalers (DPIs).
An MDI typically has a housing, which is normally an all-plastic structure, into which a metal canister with a propellant can be inserted. The correct operation of the MDI is difficult since several actions must be performed subsequently: 1) Shake the inhaler before using, 2) Priming (firing in the air) when the inhaler was not used for several days, or in some other cases (a new canister, when the MDI has been dropped etc.), 3) Breathing out sufficiently to use the Function Residual Capacity (FRC) of the lungs as much as possible, 4) Firing (firing in the mouth), 5) Inhale for a sufficient duration (several seconds) to inhale the medication, and 6) Breath-hold for a sufficient duration to keep the medication in the lungs.
Thus, many mistakes can be made using an MDI. E.g. timing between the firing and the inhalation may be wrong, or the duration of the inhalation may be too short due to a too powerful inhalation, thus preventing the medication from reaching the deepest of the lungs. It has been found that 26-70% of patients using MDIs fail to inhale slowly and deeply, i.e. inhaling within the optimal flow rate of 25-60 liters per minute.
EP 1 993 642 B1 (Bang & Olufsen Medicom A/S) discloses an MDI with a microphone positioned in an add-on device for attachment to the MDI. The microphone captures sound in the frequency range 100-3,000 Hz which is used to determine e.g. an inhaling flow velocity. However, for normal environments with background noise, such a device may not be able to provide a reliable measure of flow velocity.
WO 2014/033229 A1 describes a system for monitoring user technique of an inhaler device with a microphone for sensing sound made during operation of the inhaler device. Inhalation and exhalation breath characteristics are analysed using temporal and spectral components. Frequency components may be analysed of the identified breath sounds, and means for classifying detected sounds as an inhalation or exhalation may be comprised. A second microphone may be used in line with the first microphone in order to differentiate between exhalations and inhalations.